1. Field of the Invention
This invention relates to a device for driving an LCD device (liquid crystal display device).
2. Description of Related Art
FIG. 4 is a block diagram showing an electrical arrangement of a conventional LCD system. In FIG. 4, reference numeral 11 denotes a display memory, 12 a control circuit, 15 an LCD device, 13 a common driver for driving common electrodes of the LCD device 15, and 14 a segment driver for driving segment electrodes of the LCD device 15.
Display data stored in the display memory 11 is read out by the control circuit 12, and is sent along with clocks and frame signals to the common driver 13 and the segment driver 14. The common driver 13 and the segment driver 14 respectively supply common signals as scanning signals and segment signals corresponding to the display data to the LCD device 15. By this process, an image is displayed on the LCD device 15.
Generally, if a DC voltage is applied to a liquid crystal, an electrochemical reaction occurs at the parts of the liquid crystal which are contiguous to the electrodes, causing those parts to deteriorate. As a countermeasure, the common signals and the segment signals from the common driver and the segment driver are inverted by using a frame signal, whereby the polarities of those signals are changed every 1/2 period of the frame signal.
During a state in which an image is not displayed on the LCD device (hereafter referred to as the non-display state), the supply of the common and segment signals from the control circuit 12 to the LCD device 15 may be stopped. It often happens that the outputs of the common driver 13 and the segment driver 14 cannot be turned off. Even if the LCD device circuit is so configured that the outputs of the common driver 13 and the segment driver 14 are turned off during the non-display state, the response characteristics of the LCD device at activating the device again will deteriorate.
To prevent a deterioration of the response characteristics of the LCD device at the time of the device being activated again, there are two methods of circuit configuration by which the outputs of the common driver 13 and the segment driver 14 are not turned off during the non-display state.
A first method is to send signals corresponding to "non-lighting" from the control circuit 12 to the segment driver 14 continuously during the non-display state, and a second method is to stop the operation of the control circuit 12 and supply segment signals and common signals, which have a very little voltage difference with respect to each other, from the segment driver 14 and the common driver 13 to the LCD device 15 continuously during the non-display state.
However, according to the first method, the control circuit 12 operates during the non-display state in the same way as during the display state, so that the power consumption is not reduced. According to the second method, on the other hand, the control circuit 12 stops its operation, and therefore, the power consumption is reduced. However, since the supply of the frame signals to the common driver 13 and the segment driver 14 is also stopped, the common driver 13 and the segment driver 14 are unable to invert the common signals and the segment signals, and therefore, a DC bias voltage is applied to the LCD device 15, which accordingly deteriorates.